1. Field of the Invention
The present invention relates to a keyless entry device and, in particular, to a keyless entry device that functionally locks and unlocks a door of a car using a portable remote control carried by a car owner and an onboard control module or an onboard door controller, mounted on the car, while assuring safety of the car owner.
2. Description of the Related Art
Known keyless entry devices are conventionally employ a portable remote control carried by the owner or user of a car (vehicle) and a door control module mounted on the car. In such a keyless entry device, the portable remote control, at least, includes an operation panel on which a predetermined input operation is carried out, a function signal generator for generating a function signal in response to the operation on the operation panel, and an operation signal transmitter for converting the function signal into a wireless operation signal in the form of radiowave or infrared light to transmit it. The door control module, at least, includes a receiver for receiving the operation signal, an operation signal determining unit for determining whether the received operation signal is legal, and for generating a function signal responsive to the operation signal when the received operation signal is determined to be legal, and a door controller for locking or unlocking the door of the car in responsive to the function signal when the content of the function signal is for a door lock operation or door unlock operation.
In the keyless entry device thus constructed, the owner, at a distance from the car, operates the operation panel of the portable remote control when the owner wants locks (unlocks) a door of the car using the portable remote control. The function signal generator generates the function signal for door locking (or door unlocking) and the operation signal transmitter transmits the function signal as the operation signal to the onboard door control module. In the door control module, the receiver receives the operation signal, and the operation signal determining unit determines whether the operation signal is legal and converts the operation signal into the function signal indicative of door unlocking (door locking) when the operation signal is determined to be legal. The function signal is fed to the door controller. The door controller responds to the reception of the function signal, unlocking (locking) the car door.
In the known keyless entry device, the operation panel of the portable remote control needs to be operated, for example, a pushbutton needs to be pressed, when the car owner unlocks (locks) the car door using the portable remote control. When the owner carries a load with both hands with no free hand available to manipulate the operation panel, the owner needs to place temporarily the load somewhere or ask someone else to hold the load temporarily instead to make hands available to operate the portable remote control.
To eliminate such an inconvenience, there have been developed operation-free keyless entry devices in which a portable remote control (or a door control module or both) is designed to issue constantly an interrogating signal even with the portable remote control remaining unused. When the owner carrying the portable remote control with him or her approaches the car, an anti-theft unit or car security unit (or the portable remote control) receives the interrogating signal transmitted and senses the approaching owner, and the onboard door control module automatically puts the car door into an unlocked (or locked) state.
In the known operation-free keyless entry device, the owner having the portable remote control with him or her simply approaching the car puts the car door into an unlocked (locked) state. When the owner's hands are full, the door locking is effectively controlled. The door control module receives the interrogating signal depending on its level, and puts the car door into an unlocked or locked state. When the present location of the portable remote control, namely of the owner carrying the portable remote control is at a borderline from within which the door control module starts picking up the signal, or when an obstacle such as another car, present between the portable remote control and the door control module of own car, blocks the interrogating signal from the portable remote control and greatly changes the signal level at the door control module, the car door is frequently unintentionally switched between the unlocked state and the locked state even if the owner attempts to put the car door in the unlocked (locked) state. When the door control module of the owner car detects the proximity of the portable remote control putting automatically the car door into the unlocked state before the owner with the portable remote control actually arrives at the car, a stranger may open the car door during a short elapsed time between the unlocking of the car door and the actual time of arrival of the owner, and could steal any onboard instruments.